Canon 7D2 + Sigma 150-600 S + 1.4x II ?

[LSeries]

I just tried the 1.4x II with Sigma 150-600 S and what the hell...it worked

I mean...it even autofocuses at f/9.0 !

I thought f/8.0 was the limit, but I can't complain.

 

[AlanF]

Sure it does - in the same way as Sigma fakes the f/6.3 without the TC to be read by the Canon as f/5.6. It even produces a decent image in bright light and held very steady, with better resolution than the bare 150-600mm. But, in practice, it's hardly worth the effort for bird photography as the focus is slow and erratic. I found that the AFMA was shifted from 0 to -17 by the TC and have read accounts of it being shifted off-scale, but the this can be corrected with the Sigma Dock.

 

[LSeries]

Sure it does - in the same way as Sigma fakes the f/6.3 without the TC to be read by the Canon as f/5.6.

What do you mean by this? My camera shows f/6.3 as f/6.3.

 

[AlanF]

Sure it does - in the same way as Sigma fakes the f/6.3 without the TC to be read by the Canon as f/5.6.

What do you mean by this? My camera shows f/6.3 as f/6.3.

The Canon's AF system is told by Sigma that it is f/5.6, which enables cameras with a maximum AF f-number of 5.6 to work. The metering system is told that is f/6.3. You can fool AF cut-off mechanism manually by taping off two of the contacts, and the camera will still register the correct aperture.

 

[LSeries]

Sure it does - in the same way as Sigma fakes the f/6.3 without the TC to be read by the Canon as f/5.6.

What do you mean by this? My camera shows f/6.3 as f/6.3.

The Canon's AF system is told by Sigma that it is f/5.6, which enables cameras with a maximum AF f-number of 5.6 to work. The metering system is told that is f/6.3. You can fool AF cut-off mechanism manually by taping off two of the contacts, and the camera will still register the correct aperture.

Ok, I didn't realize there are two different values reported. Now I just wonder why limit the AF to f/5.6 when f/6.3 works just fine

 

[Ray-uk]

Sure it does - in the same way as Sigma fakes the f/6.3 without the TC to be read by the Canon as f/5.6.

What do you mean by this? My camera shows f/6.3 as f/6.3.

The Canon's AF system is told by Sigma that it is f/5.6, which enables cameras with a maximum AF f-number of 5.6 to work. The metering system is told that is f/6.3. You can fool AF cut-off mechanism manually by taping off two of the contacts, and the camera will still register the correct aperture.

This also depends on how you have your camera set, if you've chosen to use 1/2 stop settings then there is no f6.3 there is f5.6 or f6.7
Canon have chosen to state AF limits in full stops so it isn't really surprising that it will still work at f9

 

[Hector1970]

Why does Canon cut off the Autofocus at F8.
Is it that the autofocus becomes erratic or is there a more technical reason (you'd burn out the motors or something?

 

[Mikehit]

As I understand it, it is because the AF is much more unreliable.
The AF is done with the aperture wide open and at f8 the amount of light hitting the sensors is greatly reduced. Effective AF needs contrast and with lower light comes lower contrast.

But also note that Canon teleconverters report the effective aperture to the camera and it is the tc/camera programming that actively blocks AF. I have used both Kenko tc and Tamron tc and these do not report the effective aperture to the camera so AF works....well,it tries to AF but the performance is very, very poor in comparison.

I think the reason that Canon do this is that they believe they would rather have AF not work at all, and the client know exactly where they stand, than to have customers complain about erratic AF if they do not understand how it works.